1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to a self-limiting wear contact pad slider and method for making the same.
2. Description of Related Art
Fixed magnetic disk systems, typically referred to as “hard” disk drives, are now commonplace as the main non-volatile storage in modem personal computers, workstations, and portable computers. Such hard disk drives are now capable of storing gigabyte quantities of digital data, even when implemented in portable computers of the so-called “notebook” class. Many important advances have been made in recent years that have enabled higher data density and thus larger storage capacities of hard disk drives, and that have also enabled much faster access speeds, both in the bandwidth of data communicated to and from the hard disk drive, and also in the access time of specified disk sectors. Advances have also been made that have greatly reduced the size and weight of hard disk drives, particularly as applied to portable computers, have been made over recent years. These advances have resulted in the widespread availability of ultra-light portable computers, yet having state-of-the art capability and performance.
A head/disk assembly typically comprises one or more commonly driven magnetic disks rotatable about a common spindle and cooperating with at least one head actuator for moving a plurality of transducers radially relative to the disks so as to provide for the reading and/or writing of data on selected circular tracks provided on the disks. The magnetic transducer or “head” is suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator.
During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides toward the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer's ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Some fly height stability is achieved with proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
Another important factor affecting fly height is the slider's resistance to changing conditions. If the transducer fly height does not stay constant during changing conditions, data transfer between the transducer and the recording medium may be adversely affected. Fly height is further affected by physical characteristics of the slider such as the shape of the ABS. Careful rail shaping, for example, will provide some resistance to changes in air flow.
Hard drive manufacturers are starting to incorporate proximity recording type sliders in drives in order to achieve higher storage densities. The proximity recording slider is designed to maintain a small area near the read-write element in constant contact with the disk, and thus enabling smaller bit size and ultimately larger storage densities. This approach to increasing storage density puts considerable amount of strain on controlling wear at the slider-disk interface, because a slight variation in contact load and contact area could greatly affect the drive survivability.
Slider-disk contact results in lubricant depletion and degradation, wear of both surfaces, generation of wear particles, stick-slip, etc. All these phenomena affect magnetic performance of the disk drive, e.g., through jitter, as well as its durability. Nevertheless, as mentioned above, a contact slider is key for high-density magnetic recording.
As product fly heights are getting closer to the disk to increase areal density, the ultimate fly height goal will be to put the element in contact with the disk media, thus reducing the fly height to zero. However in practice, a reliable contact interface is very difficult to achieve due to the wear of the head and disk, resulting in early failure when compared to higher fly heights with a cushion of air between them. The reliability problem is exacerbated by manufacturing tolerances which results in significant variation in the amount of interference in the contact interface. Even with a product design point centered nominally at zero fly height or contact, manufacturing tolerances for both disk roughness and head fly height result in a distribution of interference such that half the interfaces will have negative (i.e., too much) interference and wear out prematurely and the other half will have positive (i.e., too little) interference and fly with an air separation which will cause poor magnetic performance.
U.S. Pat. No. 5,761,003, entitled “Magnetic head slider with crown ABS”, issued Jun. 2, 1998, to Toshiharu Sata, which is assigned to Citizen Watch Co., Ltd., and which is incorporated by reference herein, discloses a magnetic head slider including a crown air-bearing surface (ABS) adapted to be located opposite to a magnetic disk. The ABS includes a rear pad with a convexly curved upper surface, arranged at a center of the air-discharging end and longitudinally spaced from the boundary. The rear pad has such a small dimension that a dynamic pressure due to the air introduced onto the ABS is hardly applied to the rear pad. However, the slider design is not made to fly in contact with the disk such that the interference is zero over a wide range of manufacturing tolerances.
One slider design that attempts to achieve contact recording is disclosed in “An Active Slider For Practical Contact Recording”, IEEE Transactions On Magnetics, Vol. 26, No. 5, September 1990, pp. 2478–2483, by C. E. Yeak-Scranton et at. (herein referred to as “Active Slider article”). In the “Active Slider article” active material is laminated into a thin-film head to form an actuatable bender at the trailing end of the slider. The actuatable area allows the recording head to be raised or lower thereby providing contact recording when needed, but preventing rapid failure of the interface.
Nevertheless, the design is complex because it requires not only additional processing steps to add the laminated active material, but also additional circuitry to control and supply the bender drive voltage.
It can be seen then that there is a need for a simple head design that can be made to fly in contact with the disk such that the interference is zero over a wide range of manufacturing tolerances.